1. Field of the Invention
This invention relates to an improved objective lens for focusing charged particles.
2. Description of Related Art
There is an increasing need for high-resolution scanning electron microscopes in all areas of development and manufacture of micro-electronic and opto-electronic components so as to visually evaluate sub-micrometer structures, and to be able to identify deviations from standard patterns and to be able to acquire and evaluate topographical data such as heights, widths or angles of inclination. Conventional scanning electron microscopes, however, do not have the required resolution of a few nanometers unless very high accelerating voltages above about 20 kV are used which cause resist structures and integrated circuits to be damaged and non-conductive or high resistant specimens are charged which is a disadvantage.